The present invention relates to a processing apparatus for processing an object to be processed.
The conventional semiconductor device fabrication process includes oxidation processing by which the surface of silicon of a device is oxidized at a high temperature to form an oxide film (insulating film), diffusion processing by which a silicon layer with an impurity layer formed on the surface thereof is heated to thermally diffuse the impurity in the silicon layer, and other processing.
As a heat treatment apparatus for such oxidation and diffusion, a batch vertical heat treatment apparatus is known. In forming, e.g., an oxide film for a capacitance insulating film and a gate oxide film, and diffusion of impurity ions, qualities, film pressure and diffusion depths of the films are much affected by thermal budgets in cases that the films are jointed very thin, and the junctions are shallow.
As an improvement of the above-described batch heat treatment furnace a sheet heat treatment apparatus in which wafers are carried one by one on holding means into the reaction tube to a set position and quickly heated there is being studied. Such sheet heat treatment apparatus will be explained with reference to the schematic view of FIG. 7.
In FIG. 7, reference numeral 1 represents a reaction tube of transparent quartz glass, and wafer holding means 11 is disposed vertically movable in the reaction tube 1. A heat insulating member 12 encloses the reaction tube 1 on the outside thereof. Above the reaction tube 1 there is provided a heater 14 in the form of a resistance heater through a heat linearing member 13 made of, e.g., an SiC (silicon nitride) plate. Reference numeral 15 denotes a processing gas feed pipe. Reference numeral 16 indicates an exhaust pipe. Reference numerals 17a-17c represent a water jacket.
In such sheet heat treatment apparatus, essentially one sheet of wafer W is first mounted on wafer holding means 11 by carrying means in a transfer chamber below the reaction tube 1, and the wafer holding means 11 is lifted to a set position. On the other hand, the heat linearing member 13 is heated by the heater 14, and the wafer W is heated to a prescribed temperature by radiation of the heat linearing member 13. A processing gas is fed through the processing gas feed pipe 15 for, e.g., oxidation. The reacted processing gas is discharged through the exhaust pipe 16 out of the system. The reaction tube 1 and the heat insulating member are water-cooled by water supplied to the water jackets 17a -17c.
In this sheet heat treatment apparatus, the heating source for the wafer W is the plate-shaped heat linearing member 13, but in addition to heat rays radiated from the heat source directly to the wafer W, heat rays which are reflected on the inside wall of the heat insulating member 12 and radiated to the wafer W are also present. The apparatus is designed by considering only heat rays which are radiated from the heat source directly to the wafer W opposed to the heat source are considered in connection with a distance between the wafer W and the heat source, a heat quantity of the heat source, etc., whereby high uniformity of intra-surface temperature distribution of the wafer W can be secured.
Actually, however, heat rays reflected on the heat insulating member 12 are radiated to the wafer W, which makes the apparatus design very difficult to secure high uniformity of intra-surface temperatures of the wafer W. This sets a limit to improvement of the intra-surface temperature uniformity. On the other hand, as devices are increasingly integrated, patterns of the devices are more micronized, and the layers are made increasingly thinner. There is a tendency that the wafer size is increased from 6 inches to 8 inches and to 12 inches. For example, very thin films as thin as 50 .ANG. are formed on devices. In such case, some .ANG.-film thickness deflections are problems. Thus, such processing requires very high intra-surface temperature uniformity. The above-described heat treatment apparatus has found it difficult to meet the above-described requirement especially as wafers have larger diameters. A problem is consequent inevitable lower yields.